The invention relates to a method for control of an automatic transmission of a motor vehicle wherein an electronic transmission control, by means of signals proportional to wheel rotational speeds, determines a transverse acceleration value for outputting to additional program modules.
Modern automatic transmission in motor vehicles are controlled by an electronic transmission control (EGS) which for automatic selection of a stored shifting program which, as known from the publication xe2x80x9cATZ Automobiltechnische Zeitschriftxe2x80x9d 94 (1992), describes a driver type recognition, an environment recognition, a driving situation recognition, or the recognition of a manual engagement and for gear selection in accordance with situations communicates with other control units and computers of different aggregates.
An important variable for control of the automatic transmission adapted to the current operating situation is constituted by the transverse acceleration value which is calculated in the electronic transmission control.
In xe2x80x9cATZ Automobiltechnische Zeitschriftxe2x80x9d 94 (1992), pages 34 ff, is described a curve recognition whereby starting from a defined transverse acceleration, upshifts are prevented and starting from another higher transverse acceleration, downshifts are also prevented.
In order to be able to recognize the curve without an expensive acceleration sensor, the actual transverse acceleration value is calculated via an algorithm. The transverse acceleration is assessed by determining the speed differences between the non-driven curve inner and outer wheel taking into account the traveling speed.
However, identical rolling scopes of the wheels are a condition for applying the method. Said condition is constantly watched in the already known method, the curve recognition being deactivated when it is detected that the wheels have different rolling scopes.
Since the tire diameters of the wheels and thus the wheel speeds often differ from each other in the practice due to air filling of different power or on account of different profile abrasions, the calculated transverse acceleration value does not correspond to the reality, the consequence of which can be a mistaken gear selection.
Other known methods involving calculation of the transverse acceleration value are, for ex., the recognition of cornering according to DE 39 22 040 or the evaluation of a cornering according to DE 196 18 805 A1.
EP 0 694 138 B1, DE 196 18 804 A1 and DE 196 18 805 A1 have disclosed other methods for control of the automatic transmission using the transverse acceleration in which methods the tire diameters always play a decisive part in the calculation of the transverse acceleration.
In cases of different tire diameters and consequently different wheel speeds, these methods are all subject to error. In critical driving situations this can result not only in reducing the driving comfort but also in a dangerous situation.
The problem on which the invention is based is to make available a method for control of an automatic transmission of a motor vehicle in which an electronic transmission control determines by means of signals proportional to wheel speeds a transverse acceleration value for outputting to additional program modules, the transverse acceleration value being sufficiently precise even in case of different geometries and speeds of the individual wheels.
According to the invention this problem is solved by a method according to claim 1.
The inventive method offers the advantage that the transverse acceleration value required for numerous modules of the electronic transmission control can be calculated with more accuracy and yet in a simple manner via the wheel speeds.
With the inventive method are corrected divergences fro the optimum tire geometry which result, for ex., from different tire pressure, different tire profile, or different tire types so that an adulteration of the transverse acceleration value in the calculation of which wheel speeds enter are prevented.
A more precise transverse acceleration value resulting from the inventive tolerance balance of the wheels by which the wheel speed tolerance is detected and compensated prevents in turn an adulterated evaluation of the traveling situation and contributes to a precise tuning of the transmission with a shifting strategy that does justice to the situation and is adapted to the environment and to the type of driver.
In an advantageous arrangement of the inventive method it can be provided that from the wheel speeds a standardized wheel speed difference NNDO be determined which after correction by the value of a long-time filtered standardized wheel speed difference NNDF is processed as corrected standardized wheel speed difference NND in a function for calculation of the transverse acceleration value.
A great precision of the inventive method is particularly achieved when the standardized wheel speed difference NNDO is formed from a quotient of a wheel speed difference divided by the median wheel speed based on the non-driven vehicle wheels and the long-time filtered standardized wheel speed difference NNDF by means of filtering the standardized wheel speed difference NNDO over a predefined time, preferably with a low pass of the first order.